[gimp] Issue #4858 - Duplicated image shows NULL in warning when closing it

[Ell <ell src gnome org>]

commit 83f935873aebd0edf296ffe76a2d8367d1302f21
Author: Ell <ell_se yahoo com>
Date:   Mon Mar 23 22:29:34 2020 +0200

    Issue #4858 - Duplicated image shows NULL in warning when closing it
    
    In gimp_image_duplicate(), explicitly mark the new image as dirty,
    so that its dirty time is set.  This avoids showing a NULL message
    in place of the dirty time when closing the image.

 app/core/gimpimage-duplicate.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/app/core/gimpimage-duplicate.c b/app/core/gimpimage-duplicate.c
index ce8b70c9b6..857b71bb3f 100644
--- a/app/core/gimpimage-duplicate.c
+++ b/app/core/gimpimage-duplicate.c
@@ -164,6 +164,9 @@ gimp_image_duplicate (GimpImage *image)
 
   gimp_image_undo_enable (new_image);
 
+  /*  Explicitly mark image as dirty, so that its dirty time is set  */
+  gimp_image_dirty (new_image, GIMP_DIRTY_ALL);
+
   return new_image;
 }